The present invention provides methods and devices for determining an axis of upper and lower jaw articulation of a patient and modeling jaw movement about such an axis, particularly with the use of computerized visual images. The methods comprise providing digital data sets of tooth and bite configuration information which may be used to determine an estimated condylar axis of rotation for a patient. A number of data sets may be acquired and utilized for such estimations. In a preferred embodiment, data sets representing the upper jaw, lower jaw and at least two bite registers may be used to determine an axis of rotation. In an additional embodiment, data sets representing at least a first and a second bite configuration may be used to determine such an axis of rotation. Such bite configurations may be guided with the use of bite registers. The above mentioned bite registers may be formed by a number of methods and device designs of the present invention. The resulting digital data sets and axis of articulation may then be utilized to generate animated visual images of a patient""s jaws in various bite configurations throughout a given rotation around the determined axis. Accuracy of such dynamic imaging, in addition to the determination of the location of the condylar axis, may increase with the number of bite configurations recorded throughout the rotation.
In a first aspect of the methods of the present invention, digital data sets representing the upper jaw of a patient, the lower jaw of the patient and at least two bite registers may be used to determine an axis of rotation or articulation for the patient""s jaws. Digital data sets representing an object may be provided by scanning the object or a three-dimensional model of the object. The jaws of the patient may be modeled by producing a plaster cast of the patient""s teeth. After the tooth cast is obtained, it may be digitally scanned using a conventional laser scanner or other range acquisition system to produce the digital data set. A bite register may be similarly scanned to obtain a bite digital data set representing the register.
In a second aspect of the methods of the present invention, a bite register may be formed by a number of methods using a variety of bite registration devices. Bite registers may record the shape, location and orientation of the teeth of the upper jaw in relation to the teeth of the lower jaw when the jaws are in a given bite configuration. In general, it is only necessary to record the features and orientations of an adequate number of teeth to determine the orientations of the remaining teeth. Thus, bite registers are typically structures having an impression of at least a surface of a tooth in the upper jaw and a surface of a tooth in the lower jaw when the upper and lower jaws are in a predetermined bite position.
In a first embodiment, a bite register may be produced by biting a structure comprised of malleable material between the occlusional surfaces of the posterior teeth. In this case, the structure may be a block of such material having a predetermined thickness. When placed on both sides of the mouth between the posterior teeth, as described, the patient may then bite down on the blocks to record the bite configuration. Since the blocks are comprised of a malleable material, such as wax, polyvinyl silaxane, acrylic, plastic, plaster or any other suitable impression material, the teeth and associated dental features, such as gingiva, will imprint in the blocks. It may be appreciated that one continuous block may be used rather than two separate blocks, one on each side of the mouth, or any other shape and/or number of such blocks to effectively form an impression of the occlusional surfaces.
The above described methodology of forming a bite register records a bite configuration at one point in rotation of the jaws around the condylar axis. Starting from a closed position, the lower jaw rotates around the condylar axis as the bite opens to a fully opened position. A bite configuration may be registered or recorded at any point in this rotation. The point in rotation may be preselected by the thickness of the block prior to impression in the above described example. The thicker the block, the more open the bite. Thus, a series of bite registers may be formed with blocks of increasing thickness to model the bite configurations throughout the rotation or throughout a specific range of the rotation. Such a series may be comprised of two, three, four, five, or more of such bite registers, each of which may be scanned to provide a series of bite digital data sets.
In a second embodiment, a bite register may be produced by pressing a structure comprised of malleable material against the facial surfaces of the anterior teeth. It has been determined that the orientations or spatial relationships of the anterior teeth of the upper and lower jaws may adequately determine the orientations of the remaining teeth in a given bite configuration. Such a structure may be comprised of the malleable material itself, or it may be supported by a holder. The holder may be comprised of a plate, contoured to generally fit a dental arch curve, and a handle. The plate may support a malleable material, such as that described previously, and may be pressed against the facial surfaces of the anterior teeth.
Alternatively, in a third embodiment, the holder may be comprised of an upper portion and a lower portion joined by a separator to orient the upper and lower jaws in a predetermined bite position. Malleable material may be mounted on the upper and lower portions of the holder to form registration surfaces. An upper registration surface may contact a surface of a tooth in an upper jaw of a patient and a lower registration surface may contact a surface of a tooth in a lower jaw of a patient. Simultaneous contact of these registration surfaces against the appropriate teeth, by, for example, biting the registration device, may record bite information correlated to the predetermined orientation of the registration surfaces. Such orientation may be fixed or it may be adjustable to join the upper and lower registration surfaces in a series of predetermined orientations. In either case, the bite information may comprise the shape, location and orientation of at least one tooth surface in the upper jaw of a patient in relation to at least one tooth surface in the lower jaw of the patient.
Again, the above described methodology of forming a bite register records a bite configuration at one point in rotation of the jaws around the condylar axis. A bite configuration may be registered or recorded at any point in this rotation. The point in rotation may be preselected by opening the jaws to a desired configuration by any means. In the case of bite registration devices comprising a separator, the registration surfaces may be separated and oriented to open the jaws to a desired configuration based on the characteristics of the separator. The separator may join the upper and lower registration surfaces in a fixed predetermined orientation, or the separator may be adjustable to join the registration surfaces in a series of orientations. In any case, a series of bite registers may be formed to model the bite configurations throughout the rotation or throughout a specific range of the rotation. Such a series may be comprised of two, three, four, five, or more of such bite registers, each of which may be scanned to provide a series of bite digital data sets.
In a third aspect of the methods of the present invention, determination of an axis of upper and lower jaw articulation of a patient and modeling of jaw movement about such an axis may be achieved, particularly with the use of computerized visual images.
In a fourth aspect of the methods of the present invention, digital data sets representing a first bite configuration and a second bite configuration may be used to determine an axis of rotation or articulation for the patient""s jaws. This is similar to the first aspect of the methods of the present invention, described above, but utilizes different data sets to determine an axis of rotation. Rather than scanning the upper jaw, lower jaw and bite registrations separately to obtain individual representative digital data sets, the components may be assembled in a bite configuration and scanned together. For example, a plaster cast of the lower jaw may be positioned with the teeth facing upwards. A bite register may then be placed on the cast of the lower jaw, and a plaster cast of the upper jaw may be placed over the cast of the lower jaw with the teeth downwards, guided by and resting on the bite register. In this manner, the plaster casts of a patient""s upper and lower dentition to be placed relative to one another in a given bite configuration. A cylindrical scan may then acquired for the lower and upper casts in their relative positions. The scanned data provides a digital model representing an object which is the combination of the patient""s arches positioned in a first bite configuration. This may be repeated for a second bite configuration. The second bite configuration may be any desired bite configuration which is different from the first bite configuration. To accomplish this, a new bite register may be obtained from the patient in the second bite configuration. Casts of the teeth may be assembled and scanned as described above.
Once digital data sets are acquired, by any method, an image can be presented and manipulated on a suitable computer system equipped with computer-aided design software. The image manipulation may comprise rotating an image of the lower jaw around the determined axis of articulation to model the movement of a patient""s jaws. Such movement may range between a closed position and a fully open position or a portion of the range therein. The computer system may be provided with rules and algorithms which move the jaw(s) in a fully automatic manner, i.e. without user intervention. Such rules and algorithms may be based on the digital data sets representing the differing bite configuration and the determined axis of articulation.
Although a few known bite configurations may be represented, it may be desired to interpolate intermediate bite configurations between the known configurations to visually portray a range of jaw movement. Usually, the successive digital data sets representing these intermediate bite configurations are produced by determining positional differences between selected individual teeth in a digital data set of a first bite configuration and digital data set of a second bite configuration and interpolating said differences. Such interpolation may be performed over as many discrete stages as may be desired, usually at least three, often at least four, more often at least ten, sometimes at least twenty-five, and occasionally forty or more. Many times, the interpolation will be linear interpolation for some or all of the positional differences. Alternatively, the interpolation may be non-linear.
Often, the user will specify certain target intermediate bite configurations, referred to as xe2x80x9ckey frames,xe2x80x9d which are incorporated directly into the intermediate digital data sets. The methods of the present invention then determine successive digital data sets between the key frames in the manner described above, e.g. by linear or non-linear interpolation between the key frames. The key frames may be determined by a user, e.g. the individual manipulating a visual image at the computer used for generating the digital data sets.